‘Future proofing’ the central heating

Over the years we have been blessed with a very reliable heating and hot water system at Sennicotts. However that has presented a problem: because it hasn’t broken it has never been upgraded. So of the two oil boilers the newer boiler was installed in the early 1960’s. The older boiler we’re not sure about but it is a coal fired unit which has had an oil burner added.

It would appear the last major system work was undertaken by White, Bays & White Ltd (52 Grafton Way, London W1) whose two framed, typed lists of valves and their function we still have and is still useful. This work was presumably done after the second world war.

I did undertake an analysis of oil consumption which in today’s thinking I am a little embarrassed to be sharing. However we were using somewhere between 15,000 and 20,000 ltrs of kerosene annually just to heat the hot water and central heating. Of course there are plenty of much heaver users but the dissapointing bit was that neither the house nor the hot water were that warm!

The only controls we had on the system were power on and off to the boiler, a boiler thermostat and manual zoning via the valves for the heating. There were no room thermostats and no timer. The warmest rooms in the house were those adjascent to the chimney breast and a quarter of the house had no central heating.

On paper, the decision about whether to upgrade the system looked simple, especially when the oil price spiked in 2007/2008. Payback would have come in easily less than the useful life of the new equipment and was likely to be easily less than ten years.

In the end we decided to divide the decision into two seperate cases dealing with the two boilers independently. The first was the hot water system boiler which also heated two rooms with four outside walls. The second was the main heating boiler which needed to be tackled in conjunction with improving the kitchen area and adding central heating to that wing of the house.

For the heating system a heat loss calculation of over 100kW meant adding central heating to the unheated part of the house would add such demand to the heating boiler that we would need to replace the one boiler with two. This work is due in 2010.

Hot water system

New condensing boiler and hot water cylinder with three inputs and destratification circuit
New condensing boiler and hot water cylinder with three inputs and destratification circuit

Most of our effort so far has been concentrated on the ‘hot water’ system. Unchanged for decades, this was the perfect opportunity to install a system for the future. We looked at this long and hard and were keen on a number of options including gound source, air source, solar, and biomass. A woodchip boiler was ruled out because we don’t have enough woodland of our own with existing woodland maintenance costs to sink. Ground source, air source and solar all suffered from the same problem – not enough ummpph!

With cast iron plumbing throughout and no plans to replumb it was never an option to simply heat the water in a well insulated cylinder to be called off when needed. The plumbing runs are too long and the quantity of water in thick iron cold pipes would mean a long wait and a lot of wasted water each time the hot water was called on. The hot water needs to be circulated around the system and with the large surface area of the long 1″ plus pipe runs a significant amount of heat is lost. To put this in perspective 6Kw of immersion heater couldn’t get the tank to temperature with the hot water being circulated.

the satisfying sign of efficiency - the plume from the condensing boiler
the satisfying sign of efficiency - the plume from the condensing boiler

Our solution was to upgrade the system with the future in mind but to be initially heated with a condensing oil boiler and as with zoning, to give ourselves a scaleable system. The solution centred on the hot water cylinder.

Hot water cylinder.

This was designed with two key features: extra inputs and a destratification circuit.

Two extra input coils were added to the standard input giving three potential heat sources. The standard (top) coil would be heated by the condensing oil boiler. The middle coil would be spare for a future heat source (biomass, heat exchanger, or something not yet invented). The bottom coil would be for solar hot water. The cyclinder could therefore be fired by simply oil or a combination of the two main heat sources with solar topping up.

The destratification circuit was added so that in normal operation (with destratification off) the water would stratify, leaving the top of the cylinder hot and the bottom full of cold water. The advantage here is that in the morning when the cylinder calls for heat only half the tank is heated. In most circumstances the water in the top of the cylinder and the hot water pipe runs is enough to easily fill a bath. If the full tank capacity is required then a circulating pump can be manually activated which mixes (destratifies) the water in the cylinder forcing the full volume of water to be heated by the top coil.

Two immersion coils were added allowing the cylinder to run in half capacity (stratified) or full capacity.


The condensing oil boiler provided a significant efficiency saving and in itself would be the primary contributor to payback times. While the cylinder’s improved insulation and scaleabilty/flexibility would also contribute to the efficiency. The system has also been given a semi-intelligent timer and a hot water thermostat which allows control where there was none.

Asbestos lagging on the original heating system
Asbestos lagging on the original heating system

We have not arrived in the future – yet. We would have like to jump into a carbon neutral solution. However looking at the options and faced with what felt like cynical pricing when we approached companies about solutions such as ground source heat pumps (they refused to identify the costs of equipment and would only give an all in installed price) we have opted for maximum efficiency (given the design of the historic property and existing pipework) and the options to add carbon neutral heat sources without a system redesign.

We recieved an excellent service and methodical design skills from our plumber. He worked with us at all stages and I am loathed to mention his name for fear he will become too busy to ever help us with phase II but he does deserve recognition for his work and expertise! You can find Will O’Brien on yell.com under O’Brien Whittle Plumbing and Heating.


Before any work could be done the asbestos lagging needed to be removed. This was taken as a seperate decision on the basis that it had to be removed so that in the event of an emergency we would be able to find plumbers who would be prepared to work on a repair. So the asbestos was removed in Aug 2006.

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